Heating device



T. H. LENNOX.

HEATING DEVICE May 8, 1951 ori inal Filed April 23. 1949 Q \M N E Inventor Th omas H. Lennox, by W His Attorney Patented May 8, 1951 UNITED STATES PATENT OFFICE HEATING DEVICE Thomas H. Lennox, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York 3 Claims. 1

This invention relates to electric heating devices, and more particularly to electric heating devices utilizing heating units which have concentric terminals for making electrical connections thereto. This invention relates also to connection means for heating units having concentric terminals.

This application is a division of my application Serial No. 89,284, filed April v23, 1949, now Patent No. 2,515,781, issued July 18, 1950, which is assigned to the same assignee as the present application.

An object of the present invention is the provision of an improved construction for electric heating devices which incorporate heating units having concentrically disposed terminals.

Another object of the invention is to provide improved connection means for heating units having concentrically disposed terminals for making electrical connections thereto.

Still another object of my invention is to provide an improved combined handle and connection apparatus which is readily connectible to and removable from a heating unit having concentrically disposed terminals.

A more'specific object of the invention is the provision of an improved construction for soldering irons.

Other objects and advantages of the invention will become apparent as the description proceeds, and the new and distinguishing features thereof will be pointed out in the appended claims.

In carrying out my invention in one form, I provide an elongated heating unit having a threaded portion near one end and a pair of concentrically disposed terminals on that end. A hollow handle and connector apparatus is provided having an internally threaded portion for screw connection to the threads on the heating unit. Within this apparatus are resilient means for releasably connecting an electrical conductor to the outer of the concentric terminals and means including a spring and. slidable contact member for releasably connecting a second electrical conductor to the inner of the concentric terminals.

For a more complete understanding of my invention, reference should be had to the accompanying drawing, Fig. 1 of which is an enlarged view, partially in section, of a soldering iron in which is incorporated a combined handle and connector apparatus embodying my invention; while Fig. 2 is an enlarged sectional view of the soldering tip end of the soldering iron showing in detail the construction of the heating unit.

Referring to Fig. 1 of the drawing, there is 2 shown a soldering iron, designated generally by the numeral I, which is composed of two principal parts: a heating unit 2 having a soldering tip on one end and a pair of concentrically disposed terminals on the other, and a handle 3 which encloses the electrical connections to the heating unit.

The heating unit, which is illustrated in detail in Fig. 2, comprises a center electrical conductor 5 which may, for example, be made of iron wire. Surrounding wire 5 is a layer 5 of electrical insulating material which is preferably compacted magnesium oxide powder. Concentrically located around the insulation layer 6 is a tubular electrical conductor 1 of a heat resistant material which may, for example, be an alloy containing iron, cobalt and nickel. In one typical heating unit embodying my invention, tube 1 has an outside diameter of approximately .130 inch.

Around the outer surface of tubular member 1 along a portion thereof adjacent the extremity opposite the handle is a layer 8 of electrically insulating material. Layer 8 may, for example. comprise several thicknesses of insulating paper wrapped around member 1 with additional thicknesses over the extremities of member I and insulating layer 0 in the manner illustrated in Fig. 2. On the outside of insulation layer 8 is located a helical coil 9 of resistance heating wire which is preferably made of an alloy of nickel and chromium. At one end 26 of the heating coil, there are several turns of wire wound on to the outside surface of member I, while at the other end 44 several turns are coiled about center wire 5.

Immediately surrounding metal tube 1 and heating coil 5 is a layer of electrically insulating heat conductive material 10 such as compacted magnesium oxide powder. Around insulating layer l0 and enclosing all the foregoing component parts is an outer tubular metal sheath H, preferably made of an alloy of iron, cobalt and nickel. If desired, a liner 4 of mica may be provided inside sheath ll along the portion adjacent the heating coil. At the ends of sheath II are retaining members l2 and I3, which may be of baked lava, whose primary purpose is to retain insulating material [0 during and after the swaging operation, which is ex plained below.

At the end of the heating unit opposite the handle end, the soldering iron I is equipped with a copper tip portion 2'! having a' tapered wedge-shaped extremity. On this tapered wedge-shaped extremity are provided the actual soldering surfaces, such as the area designated by the numeral 28, for example. All, or a part of the outer surface of copper tip El may be ironplated, if desired, to reduce the corrosive efiect on the tip of the tin "which is contained in solder.

At the end of the heating unit adjacent the handle, the soldering iron l is provided with means for affixing the heating unit to handle 3 and for connecting the heating unit to a source of electrical energy. A cylindrical layer 29 of electrical insulation, which may, for example, be of ceramic material, surrounds tubular conductor 1 at this end of the heating unit. A cylindricallyshaped member ac, having a threaded portion 3!, is positioned outside layer 29 overlapping the end of sheath H. The threaded portion 35 engages corresponding threads on the inner surface of a bushing member 32 at the extremity of handle 3 and thereby joins the heating unit to the handle. At the inner extremity of insulator 29, there is a cylindrical member 33 of electrically conducting material, the outer surface of which provides a contact for electrical connections to tubular conductor 2. Another smaller cylindrical contact member 3% is provided at the inner extremity of center conductor 5 to provide for electrical connections thereto, with contacts-33 and 52% being separated by a suitable insulator 35 which is preferably of glass.

Referring to Fig. l, the heating unit in this typical soldering iron is connected to a source of electrical energy (not shown) by two insulated conductors H and it which are located within a protective outer sheath l9. Conductor joined to a conductive flatly disposed prong member 20, of resilient material, which is in contact with member at location when the heating unit is in the handle, thus completing an electrical connection to conductor '5 of the heating unit. Conductor i8 is joined to a conductive member 22 from which an electrical connection is completed to center conductor 5 of the heating unit through an electrically conductive coil spring 23 and a conductive slidable contact member 24. This electrical connection is made at point 36 on member 34 at the end of the heating unit when the heating unit is screwed into the handle.

There are provided within thehandle three cylindrically shaped insulators 3'], i8 and 39 which are preferably of plastic material. These coaxially disposed insulators separate the two sides of the electrical circuit from each other and from the handle, as shown in Fig. l. A resilient member ll), which is similar to member 2e, and other like resilient members (not shown) are provided around the outer periphery of insulators 31 and S8 to maintain the parts within the handle in the proper concentric relation. A coil spring 41 coacts with a flange projection 42 at the inner extremity of sheath E9 to absorb a portion of the strain on the electrical connections within the handle caused by tension on the cable made up of sheath l5 and conductors ll and i8. Bush'- ing member 52, which joins the heating unit to the handle, may be secured Within the handle 3 by means of threads 33. In addition to joining the heating unit and the handle, member 32 also serves as a retainer for the insulators and other parts within handle 3.

It will be understood that the heating unit is readily removable and replaceable in the handle merely by unscrewing threaded portion 3| from its mating member 32. Unscrewing the heating llism unit from the handle breaks the electrical conconnections automatically to be made again due to theresiliency of member 25 and spring 23 which acts on member-2d.

To construct a heating unit in accordance with my invention, I first provide a suitable length of preformed concentric electrical conductor comprising center wire 5, insulation layer 5 and outer conductor '1. The first step in the manufacturing operation is to remove a portion of outer conductor i and insulation layer 5 at each end of center conductor 5. Several thicknesses of insulating paper are then wound around the outside surface of member 7 and down over one extremityv of member 7 on to conductor 5, as illustrated in Fig. 2. Heating coil 9 is then wound on the outer surface of insulation layer 3 with several turns wound oil on member l at one end 26 and several turns on to member 5 at the other end M; or the heating coil. Following the winding of the heating coil the end turns of the coil lying on members I and 5, respectively, are staked in order to form good electrical and mechanical connections between the coil and these members.

The assembled components described in the preceding paragraph are then placed concentrically inside outer sheath M and the intervening space is filled with magnesium oxide powder. Retainers l2 and I3 are inserted at the ends of sheath H to prevent the magnesium oxide powder from coming out during the subsequent swaging operation. Member [2 has a centered opening on the inner side to admit portion 44 of the heating coil assembly, and the aperture through member i3 is also at the center so that members i2 and I3 serve to maintain the heating coil assembly on the center line of sheath ll.

After assembly in the manner described, the heating unit is swaged to compact the layer ii! of magnesium oxide powder and reduce the diameter of sheath 5 lto a predetermined value which may, for example, be .285. Sheath H is then machined at one extremity to provide for the addition of soldering tip if the heating unit is-to be used in a, soldering iron, and the soldering tip is installed. At the other end of the heating unit, members 29 and 3e are installed in this order, after which cylindrical contact 33 is' placed on tubular conductor 7 and secured thereto. Then center contact-member 3d is added and a glass seal 35 is provided between contact members 33 and 34 by the use of high frequency current to heat the glass. The heating unit is then ready to be screwed into handle after which electrical current may be circulated through the heating coil 9 to cause it to dissipate heat; The circuit which the current follows through the soldering iron I, in which this typical heating unit is incorporated, may be traced as follows, assuming that conductor i! is the forward con ductorand conductor E8 the return conductor:

conductor ll, member 2d, contact member'33,

tubular conductor ll, member 25, contact mem ber 33, tubular conductor l, heating coil 9, center conductor 5, contact member 34, member 24, spring 23, member 22, and conductor l8.

While I have illustrated and described my invention in a preferred form for use in a soldering iron, it will be readily apparent that it may be used for other purposes, such as liquid immersion heaters, for example. Also, the invention may be used in conjunction with other heating units having concentric terminals and is not limited to the specific heating unit construction described. Therefore, while I have illustrated and described one preferred embodiment of my invention, many 

